Electrostatic printing system utilizing illuminated photoconductive material



Jan. 5, 1965 J. T. MCNANEY 3,154,837

ELECTROSTATIC PRINTING SYSTEM UTILIZING ILLUMINATED PHOTOCONDUCTIVEMATERIAL med April 22, 1960 5 sheets-sheet 1 Jan. 5, 1965 .1.T. MGNANEY3,164,837

ELECTROSTATIC PRINTING SYSTEM UTILIZING ILLUMINATED PHOTOCONDUCTIVEMATERIAL Filed April 22, 1960 5 sheets-sheet 2 Jan. 5, 1965 J. T.MCNANEY 3,164,837

ELECTROSTATIC PRINTING SYSTEM UTILIZING ILLUMINATED PHOTOCONDUCTIVEMATERAL Filed April 22, 1960 5 Sheets-Sheet 3 SIGNAL SOURCE.

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Jan. 5, 1965 Filed April 22. 1960 kr--h-a--j I l r/Z J. T. MCNANEYELECTROSTATIC PRINTING SYSTEM UTILIZING ILLUMINATED PHOTOCONDUCTIVEMATERIAL 5 Sheets-Sheet 4 INVENTOR.

IBL/4% W Jan. 5, 1965 .1.1. MGNANEY 3,164,837

ELEoTRosTATIc PRINTING SYSTEM uTILIzING ILLUMINATED PHoTocoNDucTIvEMATERIA?) Filed April 22, 1960 Sheets-Sheet 5 LLM United States PatentJoseph T. McNaney, La ll/iesa, Calif., assigner to General DynamicsCorporation, Rochester, mi., a corporation of Delaware l Filed Apr. '22,19643, Sei'. No. 24,654) ld Claims. (Cl. 34e-74) This invention relatesto electrographic printing, and more particularly to apparatus forproducing an electrical. discharge whose effects can be converted toavisible display.

Luring this printing process, an electrical discharge takes placebetween two electrodes; the recording medium being positioned in thespace where the discharge occurs. As a result of the discharge eithervisible material from one of the electrodes, or a charge pattern isdeposited on the surface of the recording medium. A visible pattern maybe produced by causing the discharge to discolor the recording medium.Alternatively the disposition may produce a visible display directly, orthe resultant charge pattern may be used to attract particles of acontrasting color.

It is the principal object of my invention to provide an improved way ofproducing the electrical discharge.

The attainment of this object and others will be realized from thefollowing specification taken in conjunction with the drawings, ofwhich:

FIGURE l shows one way of producing a discharge;

FIGURE 2 illustrates the basic concept of my invention; and

FIGURES 3 9 depict various embodiments thereof.

Broadly speaking, my invention contemplates the selective stretching oflight spots so that stripes of la photoconductive material areirradiated. The illuminated pattern permits the production of anelectrical discharge at selected points, whereas the unilluminatedphotoconductor maintains a yhigh resistance-and therefore prevents adischarge.

One method of producing an electrical discharge is shown in FIGURE l.Here a potential source l is connected to a lower electrode 12, and toan upper transparent electrode 14; the latter being positionedcontiguously with a layer of photoconductive material i6. The recordingmedium 1S is positioned in the air gap between photoconductor 16 andelectrode 12.

Under normal conditions the photoconductive material is not illuminated,and its electrical resistance is high. As a result, most of thepotential appears across its thickness; and there isnt enough potentialacross the air gap to produce a discharge.

In order to initiate the discharge, a lens images light ontophotoconductor 16, causing it to assume a lower resistance at theirradiated spot. As a result, the entire potential now appears acrossthe air gap below this spot, and a discharge occurs. Actually, acomplete light pattern-corresponding to a picture or messageis imagedonto the photoconductor, producing a plurality of discharges; and thedischarge pattern therefore corresponds to the picture'or message.

It was found that frequently the discharge occurred even when thephotoconductor was not illuminated; indieating that the photoconductorwas too thin to withstand the potential. When its thickness wasincreased, the light did not penetrate the photoconductor; and theresistance was reduced only on the surface. On the other hand,increasing the air gap permitted the discharge to spread, instead ofbeing concentrated; thus degrading the resolution.

Patented `lan.y 5, i965 ICC The structure of FIGURE 2 overcomes theproblem. I-lere, for simplicity, an object-which may be a picture,amessage, eteto be copiedr is shown as transparent areas on a movingopaque medium 2l). As the medium moves, the' message is line-scanned bycylindrical lens 22, which has thecharacteristic that it elongates, lor

magniiies in only one direction; in the illustration it stretches theheight of the scan line elements without 'affecting their width. Belowthe cylindrical lens is a sheet of photoconductive material le, ontowhich is imaged the elements being scanned by lens 22 at the instant.

In the illustration, the instantaneously scanned line is througn thecenter of the word, TONE; and the elements of the letters that intersectthe scanning line are stretched to extend transversely acrossphotoconductor lo from one longitudinal edge to the other. As shown, thescanning line intersects the T at one point; and this scanned-lineelement is imaged onto the photoconductor as a sin gle, narrow,illuminated stripe. In a like manner, the scanning line intercepts the Oat two points; and these appear as two narrow, illuminated stripes onphotoconductor lo. Similarly, the three intercepts formed by thescanning, line and the N produces three narrow illuminated stripes. Thescanning line intercepts the E at the bar; and this is imaged onto thephotoconductor as a wide illuminated stripe. Thus, the scanned lineelements are converted to a stripe pattern on the photoconductor; thewidth of the stripe equaling the width of the scanned line elements. Theilluminated areas of the photoeonductor are, of course, in their lowresistance states; and conduct the potential at electrode 14 to pointsat the bottom edge otk the photoco'nductor. At these points, practicallythe entire potential is across the air gap-thus producing electricaldischarges, which in turn produce electrographic printing, or causes acharge pattern (which has been given visibility in the illustration) tobe produced on the surface of a moving recording medium 18.

As the scanning line moves across the copy, or vice versa, the patternof illuminated stripes varies. In this way the instantaneous stripepattern and the resultant instantaneous discharge pattern correspond tothe instantaneous scanning line.

The un-illuminated stripes of the photoconductor are so 'long that theirresistance does not permit the full potential to appear at the loweredge, and therefore no dischargeioccurs at these points. l f

An insulating support member 24 may be used chanical reasons.

Thus, dueto my invention, a high potential may be used for'electrographic printing; and yet in the absence of illumination, noelectrical discharge occurs.

FIGURE 3 shows another embodiment of my invention, wherein thecylindrical'lens is not used. Instead, l use a structure 25 comprisinglight guides that take the form of sheets 26. ln this embodiment, lightfrom the scanning line enters the apexes of sheets 26, and istransmitted to the far end of the sheet by internal relections. As thelight emerges from the distal edge of the sheet, it illuminates stripesof the photoconductor, in the same mannerv as previously described. Thisembodiment obviates the depth-of-foeus problem that might be associatedwith the cylindrical lens.

The embodiment ofmy invention shown in FlGURE 4 is, one wherein everyportion of photoconductive material lr6 is the same distance from thecopy; thus also obviating the depth-oi-focus problem if a lens is to beused. This embodiment shows another way of producing a scanning linewithout the use of a lens. Here the tops of light guide sheets 27 areblocked olf, except for a narrow area where light from the messageenters the light guides. The interfor me- 'nal retlections illuminatestripes of photoconductor 16 as previously described.

In the embodiments of FIGURES 1-4, the electrical discharge occurs atthe edge of the photoconductive material. If, for some reason, thiscondition is undesirable, the embodiment of FIGURE may be used. Here thedischarge occurs from the ends of probes 2S, rather than from the edgeof the photoconductor 16.

FIGURE 5 also shows another use for my invention. 'A beam of lightimpinges on an optical device 32, such as a pivotable mirror, whichchanges its orientation under control of a signal source 34. The lightbeam is "stretched as previously explained, and the illuminated stripepermits the potential at electrode 14 to be applied to a selected one ofprobes 28. The point of electrical discharge is thus established by themirror and signal source; and produces a waveform 19 on recording medium18.

It desired, the light beam 30 may be a sheet-like beam that is parallelto the pivot-axis of the mirror; whereupon lens 22 may be eliminated.

While the object to be copied has been illustrated as having transparentareas on an opaque background, it may of course comprise opaque areas ona transparent background. Alternatively, the object may comprisecontrasting lines and background; and reflected-rather thantransmitted-light may be used. Under some conditions the stripe patternwould be reversed, that is, the stripes would be un-irradiated, whilethe background would be illuminated. Under these conditions the chargepattern would be reversed; but reversing the polarity of the potentialsource and/ or the elements of the printing process would produceprinting of the desired characteristics. Therefore the term stripes willbe understood to include unradiated areas, or the irradiatedareasdepending upon the pattern.

The object to be copied may be on a film, strip of paper, sheet ofpaper, drum, loop, or similar form of medium; and the recording mediummay be similaror a strip that is later cut into separate sheets.

Still another way of presenting the object to be copied is shown inFIGURE 6. Here, the displayinstcad of being on a medium such as ofFIGURE l-appears on the face of a cathode ray tube 36; the individualscanning lines providing the instantaneous illumination which is used inthe manner previously describedwith any of the disclosed embodiments.

In FIGURE 7, the cathode ray tube has a deflection system that, insteadof producing properly proportioned characters, produces an elongatedpattern. Here again, the individual scanning lines produce theinstantaneous scanningT line elements that are to be imaged onto thephotoconductive material. The lens in this case merely collimates thelight, which is therefore projected without further distortion onto thephotoconductive material.

' In FIGURE 8, the cathode ray tube has a deflection system similar tothat described in connection with FIG- -URE 7, so that elongatedcharacters are produced on the tubes faceplate. The collimating lens hasbeen replaced by a faceplate comprising optical bers that perform thecollimating function.

FIGURE 9 shows another embodiment wherein a structure 40 of opticalfibers 41 have been formed or ground so that it has two slantingsurfaces. These surfaces have positioned thereon layers 42a and 42b ofphotoconductive material; and electrodes 44 and 46 are connected to theends thereof. The apex of structure 40 is ground off, leaving a gapbetween adjacent ends of photoconductive layers 42a and 42h. A potentialis applied to the terminals, and when each photoconductor is illuminatedby an elongated stripe-produced as described above-the potential appearsacross the gap. An electrical discharge occurs, in this way producing acharge on recording material 18.

If desired, optical iber structure 40 may be the facel plate of acathode ray tube, on the inner surface of which a phosphor ispositioned.

The invention illustrated and described herein is illustrative only andthe invention includes such other modifications and equivalents as mayreadily appear to those skilled in the art, within the scope of theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. The combination comprisingz: a sheet of photoconductive materialhaving a given width; a rst electrode in electrical contact with onelongitudinal edge of said sheet; a second electrode spaced from theother longitudinal edge of said sheet; and means responsive to theimpingement of light from a point for irradiating said photoconductivematerial in the form of a narrow transverse strip, said strip extendingfrom said first electrode across said given width to said otherlongitudinal edge-whereby a potential applied to said rst electrode maycause an electrical discharge between said second electrode and the endsof said strips.

2. The combination of claim l further comprising a source of potential,means for connecting said source between said rst and second electrodes,the potential of said source and the spacing between said otherlongitudinal edge and said second electrode being such that a coronadischarge takes place only between the irradiated arcas of saidphotoconductive material along said other longitudinal edge and saidsecond electrode.

3. The combination as set forth in claim l further including a pluralityof conductive velements each having one end in Contact with said otherlongitudinal edge of said sheet and each having the other end adjacentsaid second electrode.

4. The combination comprising: a sheet of photoconductive material; arst electrode positioned contiguously with one longitudinal edge of saidsheet; a second electrode spaced from the other longitudinal edge ofsaid sheet; means for applying a potential to said first electrode; animage to be recorded; means for line scanning said image and forprojecting light responsive to the different portions o the image alongsaid scanning line so as to irradiate parallel transverse strips of saidphotoconductive material, said strips extending from said firstelectrode to the other longitudinal edge of said sheet the width of theirradiated strips being directly related to the width along the scannedline of the corresponding portion of said image-whereby said potentialappears at the ends of said strips adjacent said second electrode andcauses an electrical discharge to take place between said ends of saidstrips and said second electrode.

5. The combination of claim 4 further comprising a source of potential,means for connecting said source between said iirst and secondelectrodes, the potential of said source and the spacing between saidother longitudinal edge and said second electrode being such that acorona discharge takes place only between the irradiated areas of saidphotoconductive material along said other longitudinal edge and saidsecond electrode.

. 6. The combination comprising: a sheet of photoconductive materialhaving two longitudinal edges; an object to be copied; means for linescanning said object; and means for causing the intercepts of thescanning line and said object to be converted to irradiated strips onsaid photoconductive material that extend transversely to saidlongitudinal edges.

7. The combination of claim 6 wherein said last means comprises a lens.4

8. The combination of claim 6 wherein said last means comprises lightguide sheets.

9. The combination of claim 8 wherein said light guide sheets have ascanning line formed by the apexes of said sheets.

10. The combination of claim 8 wherein said light guide sheets have ascanning line formed by a transparent area.

11. The combination comprising: a sheet of photocon- 5 ductive material,having two longitudinal edges; an object to be copied; means for causingthe scanning line elements of said object to be elongated so that theyform irradiated strips on said photoconductive material extendingbetween said longitudinal edges; a first electrode in electrical contactwith one end of said strips; means for applying a potential to saidfirst electrode-whereby said potential appears at said otherlongitudinal edge in the vicinity of said strips; a second electrodespaced from said other longitudinal edge; and a recording mediumpositioned be- "l'we'en said second electrode and said otherlongitudinal edge.

l2. The combination comprising: a sheet of photo conductive material,having Vtwo longitudinal edges; an object to be copied; means forcausing the scanning line elements of said object to be elongated sothat they form irradiated strips on said photoconductive materialextending between said longitudinal edges; a rst'electrode in electricalcontact with one said longitudinal edge; means kfor applying a potentialto said tirst electrode-whereby said potential appears at said otherlongitudinal edge in the vicinity of said strips; a second electrodespaced from said other longitudinal edge; and a recording mediumpositioned between said second electrode and said other longitudinaledge. l i

13. The combination of claim 12 wherein said elongation means comprisesthe deection system of a cathode ray tube. f

14. Thek combination of claim 13 wherein the faceplate of said cathoderay tube comprises optical bers.

References Cited in the file of this patent UNITED STATES PATENTS Y2,866,903 Berchtold Dec. 30, 1958 2,833,543 Wohl Apr. 2l, 1959 2,890,922Huebner June 16, 1959 2,925,310 Perkins Feb. 16, 1960

1. THE COMBINATION COMPRISING :: A SHEET OF PHOTOCONDUCTIVE MATERIALHAVING A GIVEN WIDTH; A FIRST ELECTRODE IN ELECTRICAL CONTACT WITH ONELONGITUDIANL EDGE OF SAID SHEET; A SECOND ELECTRODE SPACED FROM THEOTHER LONGITUDINAL EDGE OF SAID SHEET; AND MEANS RESPONSIVE TO THEIMPINGEMENT OF LIGHT FROM A POINT FOR IRRADIATING SAID PHOTOCONDUCTIVEMATERIAL IN THE FORM OF A NARROW TRANSVERSE STRIP, SAID STRIP EXTENDINGFROM SAID FIRST ELECTRODE ACROSS SAID GIVEN WIDTH TO SAID OTHERLONGITUDINAL EDGE-WHEREBY A POTENTIAL APPLIED TO SAID FIRST ELECTRODEMAY CUASE AN ELECTRICAL DISCHARGE BETWEEN SAID SECOND ELECTRODE AND THEENDS OF SAID STRIPS.